1. Field of the Invention
An impact absorbing type steering column apparatus with a motorized power steering device according to the present invention achieves the reduction of steering force by utilizing the rotational force of an electric motor and also achieves the protection of the seat occupant's life during a collision by the steering column being made capable of absorbing an impact during a collision.
2. Related Background Art
A steering force assisting device called a power steering device has been widely used to reduce a force (steering force) required to turn a steering wheel during a change of course. Also, in small automobiles such as light cars, an electric motor is generally utilized as the power source of the power steering device.
During a collision of an automobile, there occurs a so-called secondary collision which is the collision of the driver against the steering wheel, subsequently to a so-called primary collision which is the collision of one automobile with another automobile or the like. With a view to minimize the impact received by the driver during the secondary collision and achieve the protection of the driver's life, it has generally been practised to adopt the impact absorbing type design in which the steering wheel moves forwardly in case of the secondary collision while absorbing the impact.
As steering column apparatuses of the impact absorbing type used for such a purpose, there have heretofore been proposed ones described in various publications such as Japanese Patent Application Laid-Open No. 48-87528, Japanese Patent Application Laid-Open No. 61-57462, Japanese Patent Application Laid-Open No. 1-249571 and Japanese Utility Model Application Laid-Open No. 57-200478, and some of them have been actually used. Also, an apparatus of such structure as shown in FIG. 15 of the accompanying drawings has heretofore been conceived as an apparatus to be combined with motorized power steering.
In Figure. 15, the reference numeral 1 designates a steering shaft having a steering wheel (not shown) fixed to the upper end thereof and rotated in the direction of operation of the steering wheel, and comprising a combination of an inner shaft 2 and an outer shaft 3. This steering shaft 1 has its full length contracted by a collapsible structure, incorporated in the coupling portion of the inner shaft 2 and the outer shaft 3, when an axial impact is applied thereto.
The steering shaft 1 is inserted in a cylindrical steering column 4, which comprises an outer column 5 and an inner column 6 combined in a telescopic manner and which, when an axial impact is applied thereto, is also made into a collapsible structure which contracts its full length while absorbing this impact. Such a steering column 4 has its intermediate and lower end portions supported on a portion of a vehicle body 9 such as the underside of a dashboard by an upper support bracket 7 and a lower support bracket 8.
The upper support bracket 7 formed by bending a metallic plate is fixed as by welding to the outer peripheral surface of the intermediate portion of the outer column 5 of the steering column 4, and is supported on the vehicle body 9 through a restraining member 10 made of a slippery material.
An electric motor 11 which is the power source of the power steering device is supported by a housing 12 connected to the fore end portion of the steering column 4. A worm (not shown in FIG. 15) fixed to the output shaft of the electric motor 11 is brought into meshing engagement with a worm wheel (not shown in FIG. 15) fixed to the outer peripheral surface of the front portion of the steering shaft 1 whereby a force in the direction of rotation can be imparted to the steering shaft 1 during the electrical energization of the electric motor 11.
A connection cylinder portion 15 is formed on the rear end portion of the housing 12, and the fore end portion of the inner column 6 which constitutes the steering column 4 is fitted over the connection cylinder portion 15, whereby the steering column 4 and the housing 12 are connected together. The fore end portion of the inner column 6 is enlarged in its diameter so as to permit it to be fitted over the connection cylinder portion 15. The lower support bracket 8 is provided between the housing 12 and the vehicle body 9.
When an impact is applied to the steering wheel with a secondary collision caused by a collision accident, this impact is immediately transmitted to the steering shaft 1 and steering column 4, whereby these two members 1 and 4 are strongly axially pushed.
When the impact force thus applied in the axial direction of the steering shaft 1 and steering column 4 becomes greater than the sum total of the coupling force of the inner shaft 2 and outer shaft 3, the coupling force of the inner column 6 and outer column 5 and the coupling force of the upper support bracket 7 and restraining member 10, the upper support bracket 7 slips out of the restraining member 10 and the steering shaft 1 and steering column 4 become displaceable.
As a result, the steering shaft 1 and steering column 4 are displaced axially forwardly (leftwardly as viewed in FIG. 15) as a result of the aforementioned impact force. During this displacement, the impact applied from the driver's body through the steering wheel to the steering shaft 1 and steering column 4 is absorbed by the coupled frictional force of the inner shaft 2 and outer shaft 3 constituting the steering shaft 1, the coupled frictional force of the inner column 6 and outer column 5 constituting the steering column 4, and the plastic deformation of an energy absorbing member (not shown) provided between the outer column 5 and the restraining member 10.
An impact absorbing type steering column apparatus with a motorized power steering device according to the present invention secures the flexural rigidity of the steering column and yet increases the amount of displacement of the steering wheel, i.e., the amount of contraction of the steering shaft and steering column, during a collision accident, thereby achieving the ease of designing for security.
In the case of the conventional structure shown in FIG. 15, the fore end portion of the inner column 6 is enlarged in its diameter, and a stepped portion 34 is thus formed on that portion of the inner column 6 which is near the fore end thereof. Consequently, even when the full length of the steering column 4 is shortened with a collision accident, the full length of the steering column 4 can only be shortened by an amount corresponding to the distance s in FIG. 15 until the fore end edge of the outer column 5 strikes against the aforementioned stepped portion 34.
The simple rearward movement of the fore end edge of the outer column 5 to avoid the foregoing problem would shorten the length of mating of the outer column 5 and the inner column 6 and cause the flexural rigidity of the steering column 4 to be reduced. Such a measure therefore, cannot be adopted. Also, if the distance L between the upper support bracket 7 and the connection cylinder portion 15 were made great, the flexural rigidity of the steering column 4 could be secured and yet the aforementioned distance could be made long. However, since the distance L is limited to some extent depending on the dimensions of the various portions of the vehicle, it is difficult in design to make this distance L long.